I just converted my 1998 3500 dually crew 4wd from diesel to 7.4. When we tried to start it it will fire but then quits. I take it this could be the computer shutting it down for some reason?? The security light flashes sometime when you turn the key on and other times no. I still don't have O2 sensors on the exhaust hooked up, can that have an effect like this?

many thanks
Rick